Cmp system having an eddy current sensor of reduced height

ABSTRACT

By providing an eddy current sensor element in a polishing tool at a reduced height level in combination with a corresponding optical endpoint detection system, standard polishing pads may be used, thereby enhancing the lifetime of the polishing pad and increasing tool utilization.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the subject matter disclosed herein relates to the field of manufacturing integrated circuits, and, more particularly, to chemical mechanical polishing (CMP) process tools used for the formation of advanced metallization structures, such as so-called damascene structures, in which metal trenches and vias are formed in an insulating layer, while subsequently filling the vias and trenches with a metal and planarizing the structure by removing the excess metal using a polishing process.

2. Description of the Related Art

Typically, the fabrication of modern integrated circuits requires a large number of individual process steps, wherein a typical process sequence involves the deposition of conductive, semiconductive or insulating layers on an appropriate substrate. After deposition of the corresponding layer, device features are produced by patterning the corresponding layer with well-known means, such as photolithography and etching. As a consequence, by patterning a deposited layer, a certain topography will be created that also affects deposition and patterning of subsequent layers. Since sophisticated integrated circuits require the formation of a plurality of subsequent layers, it has become standard practice to periodically planarize the surface of the substrate to provide well-defined conditions for deposition and patterning of subsequent material layers. This especially holds true for so-called metallization layers in which metal interconnects are formed to electrically connect the individual device features, such as transistors, capacitors, resistors and the like, to establish the functionality required by the circuit design.

In this respect, CMP has become a widely used process technique for reducing “imperfections” in the substrate topography caused by preceding processes in order to establish enhanced conditions for a subsequent process, such as photolithography and the like. The polishing process itself causes mechanical damage to the polished surface, however, in an extremely low range, i.e., at an atomic level, depending on the process conditions. CMP processes also have a plurality of side effects that have to be addressed so as to be applicable to processes required for forming sophisticated semiconductor devices.

For example, recently, the so-called damascene or inlaid technique has become a preferred method in forming metallization layers wherein a dielectric layer is deposited and patterned to receive trenches and vias that are subsequently filled with an appropriate metal, such as aluminum, copper, copper alloys, silver, tungsten and the like. Since the process of providing the metal may be performed as a “blanket” deposition process based on, for instance, electrochemical deposition techniques, the respective pattern of the dielectric material may require a significant over-deposition in order to reliably fill narrow openings and wide regions or trenches in a common process. The excess metal is then removed and the resulting surface is planarized by performing a process sequence comprising one or more mechanical polishing processes, which also include a chemical component. Chemical mechanical polishing (CMP) has proven to be a reliable technique to remove the excess metal and planarize the resulting surface so as to leave behind metal trenches and vias that are electrically insulated from each other as required by the corresponding circuit layout. Chemical mechanical polishing typically requires the substrate to be attached to a carrier, a so-called polishing head, such that the substrate surface to be planarized is exposed and may be placed against a polishing pad. The polishing head and polishing pad are usually moved relative to each other by individually moving the polishing head and the polishing pad. Typically, the head and pad are rotated against each other while the relative motion is controlled to locally achieve a target material removal. During the polishing operation, typically a slurry, that may include a chemically reactive agent and possibly abrasive particles, is supplied to the surface of the polishing pad.

One problem involved in the chemical mechanical polishing of substrates is the very different removal rates of differing materials, such as of a metal and a dielectric material from which the excess metal has to be removed. For instance, at a polishing state where the dielectric material and the metal are simultaneously treated, i.e., after the major portion of the metal has already been removed, the removal rate for the metal exceeds the removal rate for the dielectric material. This may be desirable because all metal is reliably ablated from all insulating surfaces, thereby insuring the required electrical insulation. On the other hand, significant metal removal from trenches and vias may result in a trench or via that exhibits an increased electrical resistance due to the reduced cross-sectional area. Moreover, the local removal rate may significantly depend on the local structure, i.e., on the local pattern density, which may result in a locally varying degree of erosion of the dielectric material in a final state of the polishing process. In order to more clearly demonstrate a typical damascene process, reference is made to FIGS. 1 a-1 c.

FIGS. 1 a-1 c schematically show cross-sectional views of a semiconductor structure 100 at various stages in fabricating a metallization layer according to a typical damascene process sequence.

In FIG. 1 a, the semiconductor structure 100 comprises a substrate 101 bearing circuit features (not shown) and an insulating cap layer on which metal lines are to be formed. A patterned dielectric layer 102 is formed over the substrate 101 and includes openings, for example in the form of narrow trenches 103 and wide trenches 104. The dielectric layer 102 may also comprise closely-spaced openings 109. The openings for trenches 103, 109 and 104 are patterned in conformity with design rules to establish metal lines exhibiting the required electrical characteristics in terms of functionality and conductivity. For instance, the trench 104 is designed as a so-called wide line to provide low electrical resistance. The deposition of the dielectric material 102 as well as the patterning of the trenches 103, 109 and 104 is carried out by well-known deposition, etching and photolithography techniques.

FIG. 1 b schematically depicts the semiconductor structure 100 after deposition of a metal layer 105, for example a copper layer when sophisticated integrated circuits are considered. As is evident from FIG. 1 b, the topography of the metal layer 105 will be affected by the underlying pattern of the dielectric layer 102. The metal layer 105 may be deposited by chemical vapor deposition, sputter deposition or, as usually preferred with copper, by electroplating with a preceding sputter deposition of a corresponding copper seed layer. Although the precise shape of the surface profile of the metal layer 105 may depend on the deposition technique used, in principle, a surface shape will be obtained as shown in FIG. 1 b.

Subsequently, the semiconductor structure 100 will be subjected to the chemical mechanical polishing in which, as previously mentioned, the slurry and polishing pad are selected to optimally remove the excess metal in the metal layer 105. During the chemical mechanical polishing, the excess metal is removed and finally surface portions 120 of the dielectric material 102 will be exposed, wherein it is necessary to continue the polishing operation for a certain overpolish time to ensure clearance of the metal from all insulating surfaces in order to avoid any electrical short between adjacent metal lines. As previously mentioned, the removal rate of the dielectric material and the metal may differ significantly from each other so that, upon overpolishing the semiconductor structure 100, the copper in the trenches 103, 109 and 104 will be recessed.

FIG. 1 c schematically shows a typical result of chemical mechanical polishing the structure shown in FIG. 1 b. As is evident from FIG. 1 c, during overpolishing of the semiconductor structure 100, different materials are simultaneously polished with different removal rates. The removal rate is also dependent to some degree on the underlying pattern. For instance, the recessing of the metals during the overpolish time, which is also referred to as dishing, as well as the removal of the dielectric material, also referred to as erosion, is significantly affected by the type of pattern to be polished. In FIG. 1 c, dishing and erosion at the wide trenches 104, as indicated by 107 and 106, respectively, are relatively moderate, whereas at the narrow lines 103, dishing 107 and 106 are significantly increased. For obtaining a required electrical conductivity, circuit designers have to take into consideration a certain degree of dishing and erosion, which may not be compatible with sophisticated devices.

Therefore, complex control strategies are typically used in advanced CMP tools in order to generate in situ measurement data for estimating an appropriate end point of the polishing process and/or control the uniformity of the polishing process. For example, the layer thickness may be monitored at various sites on the substrate in order to determine the local removal rate during the process and/or to identify an appropriate point in time for terminating the process. To this end, optical measurement techniques, such as spectroscopic ellipsometry or other reflectivity measurement techniques, may be used. Since the optical probing of the substrate surface is difficult due to the nature of the polishing process, significant efforts have been made to provide appropriate CMP tools comprising optical measurement capabilities. For this purpose, appropriately configured polishing pads and platens have been developed that allow optical access to the substrate surface during polish. This may be accomplished by providing respective transparent windows in the pad. Respective optical measurement data may therefore be obtained for a plurality of dielectric materials and very thin metal layers during polishing, thereby enabling efficient control and endpoint detection strategies. For moderately thick initial metal layers as are typically encountered in forming metallization layers, as described above, enhanced process control may also be important during any stage of the polishing process of initially thick metal layers, which may not be efficiently addressed by presently available optical systems.

For this reason, other in situ measurement strategies have been proposed, such as sensors operating on the basis of inductive coupling. In this case, eddy currents may be induced in the metal layer, which may depend on the layer thickness. The response of a sensing coil to the eddy currents may then be used to evaluate the local thickness of the layer. Respective sensor systems may be very efficient for situations as described above with reference to FIGS. 1 a-1 c, since the metal removal may be monitored by the varying degree of induced eddy currents. Thus, advanced control regimes may be used based on optical and inductive regimes, wherein, in advanced CMP tools, both optical process control and inductive process control may be provided concurrently. For instance, respective inductive sensor portions are positioned close to the substrate surface within the pad window of specifically design polishing pads, in which the respective distance or “air gap” between the substrate surface and the sensor portion is reduced by providing a thinned material portion within the transparent pad window. This allows an efficient optical and inductive coupling during sophisticated polishing processes.

In advanced CMP techniques, an important factor is the cost of ownership for respective tools, since in the last years CMP costs have increased significantly. The delivery and management of slurries, pads, conditioners, cleansers and the like is very cost intensive. Thus, respective process and control strategies requiring special and thus expensive consumables, such as polishing pads, as described above, may have to be enhanced with respect to consumable consumption and the like, since these factors may significantly contribute to increased production costs due to frequent change of consumables, less tool utilization and availability and the like. In the case described above, the specifically designed pad may be very expensive and may suffer from a reduced life time due to window delamination and/or degradation of the thin material portion in the pad window.

The present disclosure is directed to various devices that may avoid, or at least reduce, the effects of one or more of the problems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

Generally, the subject matter disclosed herein is directed to CMP tools and related components, such as polishing pads, sensor components and the like, which enable an in situ monitoring of the polishing process, wherein at least an inductive sensor may be provided that generates a signal related to the amount of conductive material formed on a surface to be treated. As previously explained, in highly advanced CMP tools, typically optical process control and process control based on inductive sensor concepts, for instance using the eddy current principle, may be provided concurrently in order to enhance controllability and flexibility of the respective CMP tools. In these conventional CMP tools, sophisticated polishing pads may have to be used including extra thin pad windows for enabling both efficient optical coupling and efficient inductive coupling. Due to the sophisticated design of the respective polishing pad, significantly increased cost of ownership may be encountered, in particular as reduced lifetime of the corresponding window portions may require more frequent replacement of a polishing pad. In illustrative embodiments disclosed herein, a respective inductive sensor is provided that is appropriately designed to enable the usage of pad windows of increased thickness and/or standard polishing pads as are typically used in optical endpoint detection systems of CMP tools without additional eddy current sensor elements, thereby increasing the overall lifetime of the polishing pad.

In one illustrative embodiment disclosed herein, a polishing tool comprises a polishing platen having a surface configured to receive a sub pad and a top pad that comprises a polishing surface and a lower surface in contact with the sub pad, wherein the sub pad has a first opening covered by a portion of the top pad. Furthermore, the polishing tool comprises an inductive sensor comprising a sensing surface positioned to extend from the surface of the platen into the first opening, wherein the sensing surface is positioned at a height level that is less than a height level of the lower surface of the top pad.

An illustrative polishing tool disclosed herein comprises a polishing platen having a surface configured to receive a polishing pad having a substantially uniform thickness. Furthermore, the polishing tool comprises an inductive sensor comprising a sensing surface positioned to extend from the surface of the platen and to support the polishing pad.

In a further illustrative embodiment, a polishing pad for a CMP tool comprises a base material configured to be mounted on a polishing platen, wherein the base material comprises laterally restricted areas having included therein a magnetic material. The polishing pad further comprises a surface for polishing a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

FIGS. 1 a-1 c schematically illustrate cross-sectional views of a semiconductor device during various manufacturing stages in forming an advanced metallization structure using a CMP process for removing excess material;

FIG. 2 a schematically illustrates a top view of a CMP tool including an inductive sensor according to illustrative embodiments;

FIGS. 2 b-2 c schematically illustrate cross-sectional views of a portion of the CMP tool of FIG. 2 a according to still other illustrative embodiments in which a sensor surface of an inductive sensor element may be positioned at a height level that is reduced compared to sophisticated conventional CMP tools including optical and inductive sensor components;

FIG. 2 d schematically illustrates a cross-sectional view of a CMP tool comprising an optical detection system in combination with an inductive sensor element, which may be provided in a respective window of the polishing platen according to illustrative embodiments; and

FIGS. 3 a-3 b schematically illustrate cross-sectional views of a polishing pad having included therein a magnetic material according to still other illustrative embodiments.

While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.

The subject matter disclosed herein addresses the issue of increased production costs and reduced tool availability of sophisticated CMP tools or any other type of polishing tools in which advanced in situ process monitoring may be required on the basis of inductive sensor concepts. As previously explained, complex polishing processes for removing excess material and planarizing the surface topography may require precise control of the removal rate, even prior to a final polishing phase, in order to reliably control the respective polishing process. For example, during the removal of excess copper, reliable monitoring of the remaining amount of copper material may be important, even at an initial or intermediate process stage, so as to enable high removal rates without introducing undue process non-uniformities. During a corresponding polishing process, an optical detection system may be less efficient, since the corresponding reflectivity may not efficiently provide information on the remaining material amount, since the initially present surface topography may increasingly be planarized, thereby providing a highly uniform scattering behavior of the respective surface, while the remaining thickness of the metal may not allow the extraction of information with respect to the remaining layer thickness. In this case, efficient non-contact measurement techniques, for instance based on inductive principles by generating eddy currents in the metal surface to be treated, may be used for estimating the remaining material thickness, wherein the respective measurement information may also be used for determining an appropriate endpoint of, for instance, a polishing phase with high removal rate and entering a subsequent phase of reduced removal rate so as to substantially completely clear the respective dielectric surface and electrically isolating the respective metal regions contained therein. During this polishing phase, optical endpoint detection or process monitoring techniques may be efficiently used, possibly in combination with the inductive sensor components, so as to obtain a substantially uniform material removal with an efficient clearance of the respective dielectric surface portions substantially without significantly contributing to erosion of the dielectric material and dishing of exposed metal regions. Thus, in particular, the combination of optical measurement strategies and inductive sensor concepts may be highly advantageous in respective manufacturing sequences, in which highly conductive metals, such as copper, copper alloys, silver, tungsten and the like, may be formed over a patterned dielectric material, the surface topography of which has to be planarized in a subsequent step based on a polishing process. However, in addition to high process quality of respective process steps, other factors during the complex manufacturing process for forming microstructure devices are of comparable importance, such as tool utilization, tool availability, cost of ownership of respective process tools and the like, since in addition to a high production yield, the overall throughput for a given equipment may also determine the profitability of the entire manufacturing sequence. Since, in particular, polishing processes in the form of chemical mechanical polishing or electrochemical mechanical polishing and the like have significantly gained in importance during the fabrication of complex semiconductor devices, a significant reduction of cost of ownership of polishing processes in combination with an increase of tool availability may contribute to reduced overall production costs.

In illustrative embodiments disclosed herein, respective inductive sensor systems may be provided in sophisticated polishing tools without requiring extremely sophisticated and thus expensive and sensitive polishing pads, as is the case in a plurality of advanced conventional CMP tools, such as the polishing tool “Reflexion LK,” available from Applied Materials Inc. In some illustrative embodiments, a standard polishing pad including a standard pad window used for optical process control may be used wherein the corresponding sensor assembly may be appropriately adapted to the respective thickness of the standard polishing pad. In other illustrative embodiments, the corresponding height level of a respective sensing surface of an inductive sensor may be appropriately positioned in an adjustable manner so as to provide enhanced flexibility in selecting an appropriate pad configuration in sophisticated polishing tools. As a consequence, in advanced polishing tools, respective optical measurement systems and inductive sensor systems may be combined without requiring specifically designed polishing pads.

It should be appreciated that the subject matter disclosed herein may be applied to polishing tools, such as electrochemical mechanical polishing tools and the like, used for the fabrication of highly complex semiconductor devices, such as CPUs, memory chips and the like, in which advanced metallization structures have to be formed for electrically connecting circuit elements, such as transistors and the like, having critical dimensions of approximately 50 nm and significantly less. However, the principles of the subject matter disclosed herein may also be applied to any situation in which polishing tools may be used, at least temporarily, for the removal of conductive materials from respective substrate surfaces, wherein the provision of an inductive sensor system in combination with a less critical polishing pad may provide enhanced tool flexibility, in particular when the corresponding inductive sensor system may be combined with a respective optical detection system. Thus, unless specifically pointed out in the specification or the appended claims, the subject matter disclosed herein should not be considered as being restricted to polishing processes for forming copper-based metallization layers.

FIG. 2 a schematically illustrates a top view of a polishing tool 200 which may represent a CMP tool, an electro CMP tool or any other polishing tool. The polishing tool 200 may comprise a frame 210 configured to accommodate a polishing platen 220, a polishing head 230 and a pad conditioner 260, as well as any respective mechanical, electrical and other components for operating the respective components 220, 230, 260. It should be appreciated that the platen 220 may be rotatably supported by respective drive assemblies (not shown) configured to provide controllable rotation of the platen 220 in accordance with process parameters. Similarly, the polishing head 230 may be configured, in combination with any appropriate mechanical, electrical, hydraulic, pneumatic and other components, to receive a respective substrate, such as a semiconductor substrate of 200, 300 or 450 mm diameter, or any other appropriate size, and to rotate the substrate relative to the polishing platen 220 in accordance with specified process parameters, wherein a specific down force may also be applied to the substrate for obtaining a desired interaction with a corresponding polishing pad (not shown in FIG. 2 a) in combination with a respective slurry substance, such as a chemical component, an electrolyte and the like. Similarly, the pad conditioner 260 may be connected to any appropriate drive assembly in order to provide the desired positioning of a respective conditioning surface (not shown) above the polishing platen 220, thereby allowing an efficient reworking of the corresponding pad surface in order to maintain substantially uniform process conditions throughout the processing of a plurality of substrates.

The polishing tool 200 may further comprise a respective sensor portion 221 formed in the polishing platen 220, in which may be provided at least an inductive sensor 240 having a respective sensing surface 241 that may be positioned close to a corresponding surface of a substrate to be treated during the operation of the polishing tool 200. In some illustrative embodiments, the sensor portion 221 may further be configured to allow optical access of a corresponding substrate surface during the operation of the tool 200 wherein the sensor portion 221 may have an appropriately designed surface portion in the respective polishing pad that is substantially transparent for a respective wavelength range, as will be described later on in more detail.

During operation of the polishing tool 200, a substrate may be loaded onto the polishing head 230 on the basis of well-known components, such as robot handlers and the like, wherein the polishing head 230 may itself be configured to provide the respective substrate handling and transport activities within the polishing tool 200. Furthermore, the substrate loaded onto the polishing head 230 may be brought into a respective operating position and the corresponding relative motion between the polishing platen 220 and the polishing head 230 may be established on the basis of respective rotational motions of these components, wherein prior to and/or during the relative motion, an appropriate slurry substance may be supplied, which may include a chemical agent or any other component for enhancing the overall removal rate, or providing enhanced surface conditions during the corresponding polishing process. The pad conditioner 260 may be continuously or temporarily in contact with the corresponding polishing surface so as to “rework” the respective surface structure. During operation of the polishing tool 200, the sensor portion 221 may pass the substrate surface, wherein the sensing surface 241 may generate eddy currents in the substrate to be treated when a sufficiently conductive material or a magnetic material may be provided thereon. For example, the inductive sensor 240 may comprise an exciting coil and a sense coil (not shown), both of which may be coupled to the sensing surface 241, wherein the exciting coil may generate a respective varying magnetic field, which may thus cause respective eddy currents in a conductive material provided in the vicinity of the sensing surface 241 and in particular at a surface of the substrate to be treated. Thus, the electrical response of the respective sense coil may indicate the amount of conductive material located in the vicinity of the sensing surface 241, thereby providing an efficient means for estimating the corresponding polishing process in a highly dynamic manner. In other cases, the sensor 240 may comprise a single coil or a system of coils coupled to the sensing surface 241, wherein the overall inductance of the respective system may be influenced by the amount of conductive material and thus eddy currents induced therein. Consequently, upon driving the respective coil with an appropriate AC signal, the responsiveness of the coil may also be indicative of the amount of conductive material and thus of the present state of the polishing process.

As is evident, during the operation of the polishing tool 200, the respective surface of a polishing pad may interact with the substrate to be treated and the pad conditioner 260, thereby restricting the overall lifetime of the respective polishing pad. Similarly, the surface of the sensor portion 221 may come into contact with the substrate surface and the pad conditioner 260, which may significantly influence the status of the respective material covering the sensor portion 221, which may also be referred to as a window, as will be described later on in more detail. In sophisticated applications, the respective window may be comprised of a substantially transparent material having a different configuration compared to the remaining polishing surface, which may therefore be less durable compared to the remaining surface portion of the polishing pad.

In conventional devices, a respective pad window may be provided with an even reduced material thickness in order to reduce the corresponding gap between a respective sensing surface and the substrate to be treated. In this case, an even more accelerated wear of the respective window portion may be observed, thereby also reducing the overall lifetime of the respective polishing pad, even though the remaining polishing surface is still in an operable state. For this reason, the sensing surface 241 as described herein may be appropriately positioned such that an increased material thickness may be provided between the surface 241 and the corresponding substrate, thereby reducing the risk for material delamination or premature wear of the corresponding window material.

FIG. 2 b schematically illustrates a cross-sectional view of a portion of the platen 220 according to illustrative embodiments. The polishing platen 220 may have formed thereon a polishing pad 250 having a polishing surface 253 for treating a substrate surface, as previously explained. In the embodiment shown, the polishing pad 250 may be comprised of a sub pad 251 provided on a respective surface of the polishing platen 220, and a top pad 252 having the polishing surface 253 and a lower surface 254 which may be in contact with the sub pad 251. In the embodiment shown, the sub pad 251 may comprise a respective opening 251A, in which may be inserted the corresponding sensor surface 241 of the inductive sensor 240. In the embodiment shown, the sensor 240, or at least the sensing surface 241 thereof, may be coupled to a corresponding height adjustment unit 245, which is configured to appropriately adjust or vary the height level of the sensing surface 241 in accordance with respective process and device requirements. The height adjustment unit 245 may be configured to provide the respective vertical movement on the basis of any appropriate components, such as electric motors, pneumatic components, hydraulic components or any combinations thereof, as are well known for the person skilled in the art. For example, an electric motor may be coupled to a threaded member for translating the rotational motion of the electric motor into a corresponding vertical movement for adjusting the height position of the sensing surface 241. In one illustrative embodiment, the height adjustment unit 245 may be configured so as to enable the positioning of the sensing surface 241 at any height level above and below the lower surface 254, thereby providing the potential for using a variety of different types of top pads 252 having a respective window portion 252W, wherein a corresponding material thickness may vary, depending on the type of pad used. For instance, the top pad 252 may represent a highly sophisticated polishing pad as may be used in advanced polishing tools, wherein the window portion 252W may be comprised of a substantially transparent material so as to also allow the optical probing of a respective substrate surface during the processing of the device 200, as previously described. Hence, in this case, the sensing surface 241 may be positioned close to the material or in contact thereto of the window portion 252W, thereby allowing operation of the tool 200 in accordance with conventional strategies. When significantly enhanced thickness of the window portion 252W may have to be used, for instance in order to reduce material delamination or material degradation in the window portion 252W, the sensing surface 251 may be appropriately positioned so as to accommodate the respective increased material thickness.

FIG. 2 c schematically illustrates a cross-sectional view of the polishing platen 220 and the inductive sensor element 240 according to further illustrative embodiments. The top pad 252 may have a substantially uniform thickness 252T across the entire polishing platen 220 so that the window portion 252W may be provided with a respective material thickness. The top pad 252 may, in this case, be provided as a standard polishing pad designed for advanced polishing tools including optical detection systems, such as the tool “Reflexion” or “Mirra” available from Applied Materials Inc. The top pad 252 may be comprised of a microporous polymer material, such as polyurethane material, with an appropriate texture formed in the polishing surface 253 in order to generate, in combination with a respective slurry material, a corresponding polishing effect. In some illustrative embodiments, the window portion 252W may be provided as a transparent polyurethane material to enable optical endpoint technology, as previously described, while, in other illustrative embodiments, the window portion 252W may be comprised of the same material as the remaining portion of the pad 252, when optical access may not be required. Thus, the pad 252 may be provided with any appropriate thickness, for instance 80 mils and the like, substantially without requiring a material removal above the sensor portion 221, which may otherwise result in premature failure of the polishing pad 252. Hence, the sensing surface 241 may be positioned at a height level that substantially corresponds to the height level of the lower surface 254, thereby additionally supporting the window portion 252W, which may also result in enhanced uniform process conditions.

During operation of the polishing tool 200 comprising the configuration of the inductive sensor 240, as for instance shown in FIGS. 2 b and 2 c, a respective signal may be generated on the basis of an AC signal inductively coupled into a corresponding substrate surface, i.e., a conductive material provided thereon or therein, wherein the corresponding signal may be evaluated by a corresponding control unit 246. The respective gap between the sensing surface 241 and a corresponding substrate surface, which substantially corresponds to the thickness 252T in the embodiment shown in FIG. 2 c or a corresponding thickness of the window portion 252W, as shown in FIG. 2 b, may be taken into consideration during the evaluation of a corresponding sensor signal by using appropriate calibration techniques, which may include the provision of a predefined material amount above the window portion 252W so as to produce respective reference data. Moreover, respective compensation data may be deduced, which may take into consideration temperature-related effects and overall pad wear, i.e., a reduced thickness 252T, which may vary upon processing a plurality of substrates. Consequently, even for an increased gap width between the sensing surface 241 and the polishing surface 254 compared to conventional designs, in which the window portion 252W may have a significantly reduced material thickness, a reliable sensor signal may be obtained, thereby enabling advanced process control strategies while additionally providing a significantly enhanced overall lifetime of the polishing pad 252 due to the increased layer thickness and the reduced risk of material delamination at the window portion 252W.

Furthermore, in the embodiment described with reference to FIG. 2 b, sophisticated polishing pads 252 may be used, if an increased signal strength, i.e., an enhanced inductive coupling to the substrate to be treated, may be required, for instance, when conductive material layers of reduced thickness are to be treated, which may otherwise lack pronounced responsiveness to the magnetic field. In other cases, the tool may be efficiently re-configured when standard polishing pads may be used, wherein the corresponding height of the sensor element and thus of the sensing surface 241 may be appropriately adjusted on the basis of the height adjustment unit 245. In some illustrative embodiments, the height adjustment unit 245 may be operated in accordance with a corresponding wear of the polishing pad 252, irrespective of whether a standard pad, such as is shown in FIG. 2 c, or a sophisticated pad, as shown in FIG. 2 b, may be used, thereby providing the potential for substantially maintaining the resulting gap between the sensing surface 241 and the polishing surface 253. This may be accomplished, for instance, on the basis of a respective reference substrate, which may be processed on a regular basis in the tool 200, wherein a deviation from the expected signal may be compensated for by appropriately controlling the height adjustment unit 245 so as to obtain a substantial match between the measured signal and the expected signal.

FIG. 2 d schematically illustrates the polishing tool 200 according to a further illustrative embodiment, wherein an optical measurement system 270 may be arranged below the sensor portion 221, i.e., a respective opening provided in the polishing platen 220. The optical system 270 may be attached to a support member 271 which in turn may be mechanically coupled to a drive assembly 222 that is configured to rotate the polishing platen 220. The optical system 270 may comprise a light source 272 configured to emit a light beam and to direct the same to the surface of a substrate 231 that is currently being processed. Moreover, the optical system 270 may include a detector 273 that is configured and arranged to receive a light beam reflected by the surface of the substrate 231. The respective light beams may be received through a substantially transparent material provided in the window portion 252W, as previously explained. The light source 272 and the detector 273 may be coupled to a control unit 274, which is configured to evaluate the signal obtained from the sensor 273 and, if required, to appropriately drive the light source 272. Furthermore, in the embodiment shown, the control unit 274 and the control unit 246 may be connected to a tool internal control unit 201, which is configured to control respective components of the tool 200, such as a drive assembly 223 for driving the polishing head 230 and a corresponding drive unit 222 for driving the polishing platen 220.

Consequently, upon operation of the tool 200 as shown in FIG. 2 d, optical signals in combination with signals obtained by the sensor 240 may be obtained in order to provide enhanced process control and/or endpoint detection during processing of the substrate 231. In the embodiment shown in FIG. 2 d, the window portion 252W may be provided with substantially the same thickness as the remaining portion of the polishing pad 252, as previously explained, thereby providing enhanced lifetime of the polishing pad 252 and increased tool availability and utilization due to a reduced number of pad changes and maintenance activities.

FIG. 3 a schematically illustrates a cross-sectional view of a portion of a polishing platen 320 having formed thereon a polishing pad 350, which may be comprised of a sub pad 351 and a top pad 352, as previously explained. For instance, the top pad 352 may have a substantially uniform thickness, as previously described, while the sub pad 351 may have a corresponding opening 351A. Furthermore, a respective inductive sensor 340 may extend into the opening 351A. Furthermore, the top pad 352 may comprise a portion 352W which may have included therein a magnetic material in order to enhance the magnetic conductivity of the portion 352W, thereby effectively reducing a respective air gap between the sensor 340, i.e., a sensing surface 341 thereof, and the polishing surface 353. The magnetic material, indicated as 352M, may be comprised of fine particles including soft magnetic materials, such as ferrite materials and the like, which may exhibit a high electrical resistance to reduce the risk of the creation of eddy currents within the portion 352W. The respective fine particles may be provided in the form of an appropriate metallic powder or the like, and may be incorporated during the respective manufacturing process, wherein an appropriate piece of material may then be inserted into the portion 352W similarly as is typically done when providing a substantially transparent material in the portion 352W. In other illustrative embodiments, the top pad 352 may be formed on the basis of conventional techniques and the magnetic material 352M may be locally provided, thereby defining respective portions 352W within a substantially homogenous material.

FIG. 3 b schematically illustrates the polishing pad 350 mounted on the polishing platen 320 in accordance with further illustrative embodiments in which a magnetic material 351M may be provided, additionally or alternatively, in a corresponding portion 351W of the sub pad 351. Hence, the sub pad 352 may be provided without an opening at the portion 351W so that the corresponding inductive sensor 340 may be configured such that the sensing surface 341 thereof may be in contact with the portion 351W, wherein the magnetic material 351M provides the desired efficient magnetic coupling through the sub pad 351 and into the top pad 352. In this case, the mechanical strength of the sub pad 351 may be increased due to the lack of a corresponding opening required for the inductive sensor 340. If a corresponding opening has to be provided for optical access, the respective opening may be designed to comply with the requirements of the optical measurement system, while the sensing surface 341 may be covered by the material including the magnetic substance 351M. It should be appreciated that embodiments shown in FIGS. 3 a and 3 b may be combined in any appropriate manner in order to enhance the magnetic coupling to a substrate surface to be treated. For instance, in some illustrative embodiments, the magnetic material 352M may be provided within a laterally restricted area whose lateral dimension may be less compared to the sensing surface 341, thereby “focusing” the respective field lines, which may be advantageous in obtaining a scan area of reduced lateral dimensions.

As a result, the subject matter disclosed herein provides an enhanced sensor configuration for sensor systems in polishing tools based on inductive coupling, such as eddy currents, in order to avoid or reduce the necessity for applying highly sophisticated and thus expensive polishing pads with a reduced material thickness at respective pad windows. For this purpose, the height level of a corresponding inductive sensing surface may be reduced compared to conventional designs or may at least be provided in an adjustable manner, thereby providing the potential for using standard polishing pads, which may have a significantly increased lifetime compared to sophisticated polishing pads including windows of reduced material thickness. Consequently, the overall cost of ownership may be reduced and tool availability may be increased thereby contributing to an enhanced overall throughput.

The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. 

1. A polishing tool, comprising: a polishing platen having a surface configured to receive a sub pad and a top pad, said top pad having a polishing surface and a lower surface in contact with said sub pad, said sub pad having a first opening covered by a portion of said top pad; and an inductive sensor positioned in said first opening, said inductive sensor having a sensing surface that is positioned at a height level that is less than a height level of said lower surface of said top pad.
 2. The polishing tool of claim 1, wherein said top pad comprises a substantially transparent window.
 3. The polishing tool of claim 2, wherein said window is positioned above said first opening in said sub pad.
 4. The polishing tool of claim 2, wherein said window is positioned above a second opening formed in said sub pad.
 5. The polishing tool of claim 1, wherein said sensing surface is substantially flush with a surface of said sub pad that is in contact with said top pad.
 6. The polishing tool of claim 1, further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material above said top pad.
 7. The polishing tool of claim 2, further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said top pad.
 8. The polishing tool of claim 1, wherein said top pad comprises a magnetic material at a portion located above said sensing surface.
 9. The polishing tool of claim 1, further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface.
 10. The polishing tool of claim 1, wherein a thickness of said top pad is substantially uniform across said polishing platen.
 11. A polishing tool, comprising: a polishing platen having a surface configured to receive a polishing pad having a substantially uniform thickness; and an inductive sensor comprising a sensing surface positioned to extend from said surface of said platen and to support said polishing pad.
 12. The polishing tool of claim 11, further comprising a sub pad provided below said polishing pad, said sub pad having at least one opening for receiving said sensing surface.
 13. The polishing tool of claim 11, wherein said sensing surface is covered by a window portion of said polishing pad.
 14. The polishing tool of claim 11, further comprising a control unit coupled to said inductive sensor to obtain a signal responsive to the presence of a conductive material provided above said polishing pad.
 15. The polishing tool of claim 13, further comprising an optical measurement system optically coupled to said window for optically probing a surface portion of a substrate placed on said polishing pad.
 16. The polishing tool of claim 11, wherein said polishing pad comprises a magnetic material at a portion supported by said sensing surface.
 17. The polishing tool of claim 11, further comprising a height adjustment unit coupled to said sensing surface and configured to vary a height of said sensing surface.
 18. A polishing pad for a polishing tool, comprising: a base material configured to be mounted on a polishing platen, said base material comprising laterally restricted areas having included therein a magnetic material; and a surface for polishing a substrate.
 19. The polishing pad of claim 18, wherein said magnetic material is comprised of ferrite particles. 